Membrane transport of long chain fatty acids (FA) in the isolated adipocyte can be stimulated up to 15 fold by catecholamines (Abumrad et al. J.B.C. 260, 9969 (1985) and ACTH (unpublished observations). Insulin on the other hand can completely suppress the catecholamine stimulation (Abumrad et al. J.B.C. (1986) in press). The action of catecholamines is mediated by activation of adenylate cyclase and of cAMP dependent protein kinase. In the case of insulin a decrease in cAMP levels seems necessary but is not sufficient to explain its mechanism of action. Our findings support the view that membrane transport of fatty acids is a major regulatory step in lipid mobilization. We wish to extend our work to determine the mechanism of transport regulation. We will investigate the contribution of events like phosphorylation of membrane protein, modulation of the carrier number or of its subcellular distribution, and that of cAMP independent pathways. We will determine the significance of transport regulation with regard to metabolic stress and disease like with fasting and diabetes. The possibility that slow acting lipolytic hormones like growth hormones and glucocorticoids control the synthesis of the carrier protein will be investigated. Effects observed could be used in future studies to isolate the mRNA that codes for the transporter. A major effort will be devoted to identification and isolation of the carrier protein. This will involve standard chromatographic procedures, high pressure liquid chromatography and immunological approaches. When a FA-binding protein has been isolated many of its properties can be studied and related to its transport function (subunit structure FA binding, phosphorylation by protein kinase---etc.). In summary the work proposed will characterize a newly described regulatory mechanism in lipid mobilization. It should have relevance to many clinical situations. Abnormalities of FA metabolism are prevalent in obesity and diabetes. Fasting and exercise are associated with acute and essential changes in FA mobilization. The facilities available to conduct the work are excellent. Also tremendous expertise in transport regulation, protein chemistry, immunology, and molecular biology exists among the various faculty members. Advice and help are readily available which greatly enhances the prospects of quick progress.